用java编写一个简单的字符串加密解密程序，将字符串分成若干行，实现字符串以一列一列读取，并还原之前输入的字符串。这里实现4行输出。

package com.java.str;

import java.util.Scanner;

public class str_chg {

public static void main(String[] args) {
// TODO Auto-generated method stub
Scanner sc = new Scanner(System.in);
String str = null;
System.out.println("请输入您想输入的字符串：");
str = sc.nextLine();
int nStr = str.length();
char[] a_str = new char[nStr];
a_str = str.toCharArray();
//System.out.println(a_str);
char[][] b_Array = new char[4][nStr];
//加密设计
b_Array[0][0] = '3';
for (int i = 1; i < 4; i++){
for (int j = 0, k = i - 1; j <nStr && k < nStr ; j++, k+=3){
b_Array[i][j] = a_str[k];
}
}

for (int i = 0; i < 4; i++){
for (int j = 0; j < nStr; j++){
System.out.print(b_Array[i][j]);
}
System.out.println();
}

for (int i = 0; i < 4; i++){
for (int j = 0; j < nStr; j++){
System.out.print(b_Array[i][j]);
}
}

//解密设计
char[] b_str = new char[nStr];
int k  = 0;
for (int m = 0; m < nStr; m++){
for (int n = 1; n < 4 && k < nStr; n++){
b_str[k++] = b_Array
[m];
}
}
System.out.println();
for (int i = 0; i < nStr; i++){
System.out.print(b_str[i]);
}
}
}